The long term goal of the proposed research is to identify factors that influence the incidence of breast cancer and to exploit this information in research into methods of preventing the disease. Specifically, it is proposed to determine whether plasma levels of lipids and lipoproteins are related, as previous work has suggested, to familial risk of breast cancer. The purpose of the proposed study is solely to determine whether a relationship exists between the concentration of plasma lipids and familial risk of breast cancer and not at this stage to determine whether any such association is genetic in origin. It is predicted that HDL-C will be elevated and TG depressed in women who are members of families at increased risk of breast cancer compared to female members of families who are not at increased risk of the disease. Families will be selected from the extensive pedigrees that have been compiled for patients with breast cancer at Creighton University. These pedigrees will be used to identify 2 types of families. One in which at least 2 first degree relatives have developed breast cancer (referred to as familial breast cancer) and another in which breast cancer has occurred in only 1 women in at least 3 generations (referred to as sporadic breast cancer). Families with familial breast cancer will be matched with families with sporadic breast cancer according to the age at diagnosis of the case. The unaffected first degree female relatives of the breast cancer cases in the families so identified will then be asked to participate in a study and measurement made of demographic, epidemiological, and nutritional data and fasting blood obtained for measurement of plasma lipids. Female members of pairs of families (sporadic and familial) at different risks for the development of breast cancer will then be compared to determine whether evidence exists of an association between familial risk of breast cancer and plasma lipid level. The influence of other variables on any association that is found will then be examined. These variables will include body weight nutritional intake, alcohol consumption, hormone use, and smoking status.